Wheel arches are known as sources of noise because of the vibration and the impacts to which they are subjected while the vehicle is running.
A known solution for attenuating this phenomenon consists in replacing the rigid portion of the wheel arch that is exposed to projections coming from the rotating tire with a mat which serves to damp the impacts and the vibration to which it is subjected.
For example, German patent DE 1 981 756.7 discloses a wheel arch constituted by a body made of thermoplastic material and by a mat which occupies that portion of the body which is situated radially outwards from the wheel when the wheel arch is mounted on the vehicle.
The mat is subdivided into rectangles that are held by their edges, which are embedded in the body of thermoplastic material, which body includes strips of material between the mat rectangles.
These strips perform a stiffening function serving to prevent the mat from collapsing over the wheel, and secondly to stiffen the body as a whole, and thus to stiffen the wheel arch.
One of the advantages of such a wheel arch is that it can be made using a single injection molding operation, with the connection between the mat and the thermoplastic material being the result of the thermoplastic material in the molten state infiltrating into the thickness of the mat at the time of injection.
Nevertheless, that method suffers from the drawback that the molten thermoplastic material tends to infiltrate into the thickness of the mat beyond the edges of the rectangles.
In particular, the compacting stage accentuates this undesirable phenomenon of material infiltrating into the mat. The compacting stage is the second stage of the injection molding method, which method begins with a stage in which the mold is filled with molten material, followed by a stage in which said material is compacted, during which stage no additional material penetrates into the mold, but the pressure of the material is increased so as to ensure that the part retains its shape while the material is solidifying.
In addition, the mat can facilitate this infiltration if it includes non-uniformities in thickness or in density.